1. Field of the Invention
The invention relates to a method for optical time-division multiplexing and to an optical time-division multiplexer, having at least one multiplex element, in which at least two optical inputs are connected via a junction to an optical signal output, and having an optical transmitters.
2. Background Information
In optical digital transmission systems, the bit rate is rising continuously. Target values for the future are on the order of 30 to 50 Gbit per second. Since with known direct-modulated semiconductor lasers, such target values are attainable only with very great difficulty, signal streams generated by individual semiconductor lasers are combined in an optical time-division multiplexer to make a signal stream with a higher bit rate.
One such system is known from Electronics Letters, Nov. 19, 1987, Vol. 23, No. 24, pages 1270 and 1271. In the known system, an active 3 dB Ti:LiNbO.sub.3 switch is used as a time-division multiplexer.
In the known system, the signal streams are generated by so-called phase-coupled semiconductor lasers, which have a predefined phase relationship with one another. Phase-coupled semiconductor lasers of this kind have the characteristic that although they produce very short pulses, nevertheless two successive pulses are spaced apart by a time interval that is approximately 10 times as long as the pulse duration. The pulses generated have a pulse duration of 15 ps and are switched through in time intervals having a length on the order of 62.5 ps. The various pulses are in a phase relationship such that they are distributed uniformly. Accordingly, only the particular time interval in which the pulse is located needs to be switched through at a given time. This system runs up against its limits if two successive pulses of a signal stream follow one another directly, without a long time interval between them.